The use of a nickel-zirconia cermet fuel electrode for solid oxide electrolyte electrochemical cells is well known in the art, and taught, for example, in U.S. Pat. No. 4,490,444 (A. O. Isenberg). This electrode is approximately 50 micrometers thick, and contains nickel particles embedded in a zirconia skeletal structure. This fuel electrode or anode must be compatible in electrical, and physical-mechanical characteristics, such as thermal expansion, to the solid oxide electrolyte to which it is attached, and must be also be chemically resistant to contaminants, such as sulfur, found in contacting fuel feed gases. In U.S. Pat. No. 4,702,971 (A. O. Isenberg), an attempt was made to provide a sulfur resistant fuel electrode by coating the fuel electrode with an ionic-electronic conductive coating containing doped or undoped cerium oxide or doped or undoped uranium oxide, where the dopants were zirconia, thoria, or lanthanide oxides. The coatings were applied over "large", 1 micrometer to 5 micrometer conductor particles, in a zirconia skeleton, as salt solutions of the metal oxide coating desired. Such coatings solved sulfur tolerance problems, but even further improvements of the fuel electrodes are needed.
It is a main object of this invention to provide improved fuel electrodes for solid oxide electrolyte electrochemical cells.